Fire control computer



' Aug. 29, 1944.

G. A. cRowTl-IER FIRE CONTROL COMPUTER Original Filed Feb. 11, 1941 2Sheets-Sheet l RHS INVENTOR Georqe. Ulwwhmf- A TTORNE Y @EMM m Aug. 29,1944.

235. BEGlSTEBS.

Patented Aug. 29, 1944 @Smidt UUE FIRE CONTROL COMPUTER George A.Crowther, Manhasset, N. Y., assigner to Ford Instrument Company, Inc.,Long Island City, N. Y., a corporation of New York Original applicationFebruary 11, 1941, Serial No.

378,367. Divided and this application November 30, 1942, Serial No.467,339

Claims.

, This application is a division of application Serial No. 378,367,iiled February 11, 1941.

'I'his invention relates to gun-re control computers and particularly tothat type of computers used to control the ring of guns againstaircraft.

The problem of the control of gun-fire against aircraft may be dividedinto two classes; (1) Where the aircraft or target is approachingdirectly towards its objective or the point of observation and thefiring gun, and (2) where the target is passing at a distance to oneside or the other of the observing and ring point. The invention hereindisclosed is applied to the first mentioned class. that some of theprinciples thereof are applicable to the solution of problems of thesecond mentioned class.

In considering the solution of the problem of anti-aircraft lire controlto which this inventionI is applied as one embodiment thereof, it isassumed that the target is directly approaching its objective, which isthe point of observation and the point of ring of the gun, at asubstantially constant height above the horizontal plane of theobjective, such as would be done in horizontal-bombing of a selectedpoint. Upon the picking up of the target by observers at the objective,the direct or slant range of the target and its elevation above thehorizontal, expressed in angular units, are observed by instruments wellknown in the art and from the observed data the height of the target andthe horizontal range may be determined, or if the height of the targetis known or obtained by observations and the elevation is observed, theslant range and the horizontal range may be determined.

From experimental data obtained during target practices, the mosteiective ranges of the guns are known as well as the time in secondsrequired to set and adjust the sights and the fuses of the projectilesand to load and re the projectiles. In this specification, the time re-.quired to set the observed values into the mechanisms, for themechanisms to calculate the advance range or fuse setting and the sightangle, and the time required to adjust the sight and gun and load andfire the gun is defined as the preparation period of time. Thispreparation period is arbitrarily selected and is based upon experienceunder various circumstances of operation.

The object of the invention is to provide a mechanism settable inaccordance with an observed range or height and elevation angle of Itwill of course be understood an approaching aircraft target and settablein accordance with the speed of the target and the selected preparationperiod of time following the instant of the observations, for computingthe sight angle or difference in elevation of the gun and the line ofsight at the instant of iiring and the time-setting values of the fusesof the fired projectiles.

Mechanisms for accomplishing the objects of the invention and theiroperation will be understood by considering the following descriptionand accompanying drawings in which:

Fig. 1 is an elevation side view of an aircraft target directlyapproaching an observing and ring point at a constant height and showingthe consecutive angular and linear relations of the target to theobserving and firing point; and

Fig. 2 is a diagrammatic View of a mechanism to compute the valuesrequired in the control of the lire of the gun.

Referring particularly to Fig. 1, an aircraft or target I is directlyapproaching the observing and ring point O at a constant height (H)above the horizontal O-O' and at a horizontal speed of St.

When the target I reaches point A, observers at O observe the direct orslant range (R) and the elevation angle of the target (A1), from whichthe height (H) and the horizontal range (RH) may be calculated by theequations resulting from the right angle triangle OAA of H=R sin AI andRH=R cos AI, respectively. A is the projection of the point A on thehorizontal 0---0 The preparation period of time (X) is selected asrequired and multiplied by the speed of the target (St) to give thedistance traveled by the target during the time (X) represented by thelength of line AB, thus defining the point B at which the target I willbe at the end of the preparation period. The value of the distance ABmay be expressed by the equation The horizontal range of target I atpoint B (RHS) is equal to the observed horizontal range minus thedistance AB or From the right angle triangle OBB', the elevation of thetarget when at point B (A3) will be the angle whose tangent is theheight divided by the horizontal range to the point B, or

From ballistic tables or curves obtained from experimental data the timeof flight (t) of projectiles is known for various combinations ofhorizontal ranges and heights. As is well known the time of ight (t) isthe period of time between the instant of firing of the projectile andthe instant of its intercepting the target. The travel of the targetduring this period of time is equal to the speed of the targetmultiplied by the time of flight or t'St, and is indicated on Fig. 1 bythe line BC, or l This distance determines the point of `intercept (C)and a perpendicular dropped from C determines the point C'. It isobvious that OC represents the horizontal range to the point ofintercept (RH2) and that The elevation angle of the point of intercept(A2) is obtained from the right angle triangle OCC and is the anglewhose tangent is the height divided by the horizontal range to the pointof intercept (RH2) or H A2-tan 1RH2 (6) The elevation of the gun abovethe line of sight to the point B, to allow for the movement of thetarget during the time of flight is known as vertical angular deflection(Ut) and may be ex- Dressed as Ut=A2-A3 (7) It is obvious that thedistance AC is equal to (X-l-t) St and that Also from ballistic tablesand curves obtained from experimental data the correction in elevation,known as super elevation (e) that must be applied to `compensate for theshape of the trajectory of the projectile, is known for variouscombinations of horizontal ranges and heights. The total elevation ofthe gun above the line of sight is known as sight angle (Us) and may beexpressed as The mechanism required for the mechanical solution of theproblem as set forth in detail hereinbefore is connected as a closed orregenerative system, that is, one section of the mechanism modifies orpartially controls the movement of a second section, and the output ofthe second section is combined in or partially controls the movement ofa third section and the output movement of the third section isconnected back to affect or modify the movement of the first or secondsection. Such mechanisms as a system are stable and operable,`when themovement thus connected back to modify the input to a preceding sectionis only a small part of the total input to that section and thereforehas a much reduced effect on the output of the section which isconnected back.

Referring particularly to Fig. 2, the vector inputs of the vectoranalyzer or component solver 2 are the observed direct range (R) set inby handle 3 and shaft 4 and the observed elevation of the target (A1)from the point of observation (O) set in by handle 5 and shaft 6. Theset in values of R and A1 are made visually available by dials 'I and 8geared to shafts 4 and 6, respectively. The outputs of component solver2 are shafts 9a and I D, the rotational positions of which representheight (H) and horizontal range (RH), respectively. Shaft 9a isconnected to shaft 9 through differential 9b the third side of which isshaft 9c to which is geared zero reader dial 9d.

Shaft 9 is moved by handle 9e to set the value of height into the restof the mechanism, by bringing the zero reader dial 9d to its zeroposition by the connection of shaft 9 to the differential 9b. The valueof height (H) set into'the mechanism is indicated by the dial 91 gearedto shaft 9. If height is known, instead of range, the height is set inby handle 9e and dial 9i to the observed value. Any displacement of thezero reader dial is removed by operating the range handle 3 to bring thezero reader dial back `to zero. This will introduce a value of range (R)corresponding to the value of elevation A1 and height (H) set into themechanism.

The inputs of the conventional multiplier I2 are the estimated speed ofthe target (St) setV in by handle I3 and shaft I4 and the sum of thepreparation time (X) and the time of flight (t). The value of X is setin by handle I5, shaft I6, differential I1 and shaft I8. The set invalue of X is made visually available by dial I9 geared to shaft I6. Theset in value of St is made Visually available by dial I4a geared toshaft I4. The generation of the value of the time of flight (t)represented by the rotation of shaft 20 will be described hereinafter.

The output of multiplier I2, (X -I-t) St, is transmitted by shaft 2| todifferential 22 where it is combined with the motion of shaft I0representing horizontal range (RH). 'I'he output of differential 22,RH-(X-i-T) St or RH2 (see Equation 8) is transmitted by shaft 23 to aconventional three-dimensional cam unit, or which the other input isshaft 9 representing height (H). Cam 24 of this unit consists of a solidrotated by the shaft 23 representing horizontal range (RH2). Thesurfaces of the various lateral cross-sections of the solid along itsaxis form a cam surface to give to cam follower 25 a motion proportionalto the time of flight of the projectile for the range represented by therotational position of the cam andthe value of height represented by theaxial position of the follower 25. The cam follower 25 is positionedparallel to the axis of the cam 24 to engage the various lateralsections of the solid cam in accordance with the value of height (H) asrepresented by rotational position of the threaded portion of shaft 9,which engages the threaded carriage on which follower 25 is mounted forrotational movement. Cam follOWer 25 is kept in engagement with the camsurface by spring 26 and its motion is transmitted to elongated gear 21on shaft 20 by the toothed sector 28 to which follower 25 is secured.Shaft 20 is connected to differential I1 to introduce time of flightinto multiplier I2 as previously described.

Shaft 23 representing horizontal range (RH2) is also connected as oneinput to position one of the component slides of a conventional vectorsolver 29. The input for positioning the other component slide of theVector solver is shaft 9 representing height (H). The output of vectorsolver 29 is shaft 30, which is driven by the vector gear, therotational position of which represents the angle of the point ofintercept (A2), as shown by Equation (6). The vector gear is providedwith a radial slot in which is slidably mounted a pin 29a which projectsthrough slots in the component slides. The radial position of the pin29a Z631 tltiii l trib.

and the angular position of the vector gear are determined by theintersection of the component slides.

The inputs of the conventional multiplier 3| are shaft I4 representingtarget speed (St) and shaft 20 representing time of flight. The outputof multiplier' 3| is shaft 32 the rotational position of whichrepresents t-St. The motion of shaft 32 is combined with that of shaft23 rep-f resenting horizontal range (RH2) by differential 33 and theoutput of differential 33, shaft 34, is connected to vector solver 35 asone input thereto, the other input being shaft 9 representing height.The output of vector solver 35 is shaft 36, the rotational position ofwhich represents the value of the elevation angle of the point of firing(A3). The value of A2 minus A3 is obtained by connecting shafts 30 and36 to differential 31, the output of which is shaft 38. The rotationalposition of shaft 38 represents Ut (see Equation '1).

The value of the super elevation (e) is obtained by the threedimensional cam 39, which is similar in construction and operation tocam 24, except the surface of cam 39 is such that the radial positionsof the cam follower 4|) relative to shaft 23 represent super elevation(e). The position of the cam follower 40 and the associated toothedsector controls the rotational position of the elongated gear 4| inaccordance with the value of the super elevation (e) corresponding tothe values of horizontal range and height represented by shafts 23 and 9respectively.

The motion of shaft 42 which is driven by elongated gear 4| is combinedwith that of shaft 38 by differential 43, the output of which, shaft 44,represents the sight angle (Us). The sight angle is made visuallyavailable by dial 45 geared to shaft 46 which is connected to shaft 44by differential 41. Arbitrary corrections in sight angle may be appliedto shaft 46 by shaft 48 which is connected to differential 41, the otherinput of which is shaft 44. Shaft 48 is moved by handle 49. The Valuesof the corrections are made visually available by dial 58 geared toshaft 48.

As the fuses of the projectiles are set in accordance with the time offlight (t), shaft 20 is connected to graduated dial 5l by differential52 and shaft 53. The other input to differential 52, shaft 54, isprovided to apply arbitrary corrections to dial 5|. Shaft 54 is moved byhandle 55. The values of the corrections are made visually available bydial 56 geared to shaft 54.

It has been found that the deflection due to the drift of a projectileis substantially proportional to the super elevation (e) of the gunrelative to the line of sight. Therefore dial 51, suitably calibratedfrom experimental data to give values of drift for corresponding valuesof super elevation, is connected to shaft 42 by shaft 58 through .g

differential 59. Corrections in deflection may be added by moving handle60 on shaft 6| which is connected to the third side of differential 59.The value of the corrections in deection is vmade visually available bydial 62 geared to shaft It is obvious that various changes may be madeby those skilled in the art in the selections of mechanisms and mode ofoperation within the scope of the following claims.

I claim:

1. A closed system fire control computer, for a gun firing at a targetapproaching at a constant height above a horizontal plane, comprising avector analyzer including a settable vector member representative of thedirect range and elevation angle of the target position at an observinginstant and component members movable to positions representative of thehorizontal range and height components of the target position, amultiplier settable in accordance with the sum of a selected preparationperiod of time and the period of the time of flight of the projectileand the speed of the target for positioning an output in accordance withthe change in horizontal range during the combined preparation andflight periods, a second multiplier settable in accordance with theflight period and the speed of the target for positioning an output inaccordance with the change in horizontal range of the target during theperiod of time of flight of the projectile, means for combining themovements of the outputs of said multipliers and the movement of thehorizontal range member for moving a pair of elements in accordance withthe horizontal ranges of the target at the end of the respectiveperiods, a pair of vector means settable by the movements of therespective elements and the height member of the vector analyzer fordetermining the angles of elevation of the target at the end of therespective periods, means for combining the outputs of said pair ofvector means for determining the vertical angular deflection, andballistic computing means settable in accordance with the position ofthe element representing the horizontal range of the target at the endof the flight period and in accordance with the height member fordetermining the super elevation of the gun and the flight period, andmeans operably connecting the output of the ballistic computing meansrepresenting the flight period to the input members of the saidmultipliers settable in accordance with the period of time of flight ofthe projectile.

2. A closed system fire control computer, for a gun firing at atargetapproaching at a constant height above a horizontal plane,comprising a vector analyzer including a settable vector memberrepresentative of the direct range and elevation angle of the targetposition at an observing instant, a first component slide movable to aposition representative of the horizontal range component of the targetposition and a second componentslide movable to a positionrepresentative of the height component of the target position, meanssettable in accordance with a selected preparation period of time, meansmovable in accordance with a computed period of time of flight of theprojectile, a rst differential for combining the movements of thepreparation period means and the ight period means, a first multiplierconnected to the output of the first differential means and alsosettablein accordance with the speed of the target. a seconddifferential for combining the output of the first multiplier and themovement of the first component slide, a first ballistic computing meanssettable by the said second component slide and the output of the seconddifferential for determining the flight period, means connecting theoutput of the first ballistic means to the flight period movable means,a second multiplier settable by the flight period movable means and inaccordance with the speed of the target, a third differential forcombining the output of the second multiplier and the output of thesecond differential, a first vector means settable by the output of thethird differential and the movement of the said second component slide,a second vector means settable by the output of the second differentialand the movement of the said second component slide, a fourthdifferential for combining the outputs of the first and second vectormeans for obtaining the vertical angular deflection, a second ballisticcomputing means settable by the said second component slide and theoutput of the second differential for determining the super elevation ofthe gun, and a fifth differential for combining the outputs of thefourth differential and the second ballistic means whereby the output ofthe ilfth differential represents the desired elevation angle betweenthe gun and the sight.

'3. A closed system fire control computer, for a gun firing at a targetapproaching at a, constant `height above a horizontal plane, comprisinga vector analyzer including a settable vector member representative ofthe direct range and elevation angle of the target position at anobserving instant and component members movable to positionsrepresentative of the horizontal range and height components of thetarget position, a multiplier settable in accordance with the sum of aselected preparation period of time and the period of the time of flightof the projectile and the speed ofthe target for positioning an outputin accordance with the change in horizontal range during the combinedpreparation and flight peri- 4 ods, a second multiplier settable inaccordance with the flight period and the speed of the target forpositioning an output in accordance with the change in horizontal rangeof the target during the period'of time of flight of the'projectile,means for combining the movements of the outputs of said multipliers andthe movement of the horizontal range member for moving a pair ofelements in accordance with the horizontal ranges of the target at theend of the respective periods, a pair of vector means settable by themovements of the respective elements and the height member of the vectoranalyzer for determining the angles of elevation of the target at theend of the respective periods, means for combining the outputs of saidpair of vector means for determining the vertical angular deflection,

ballistic computing means settable in accordance with the position ofthe element representing the horizontal range of the target at the endof the flight period and in accordance with the height member fordetermining the flight period, and means operably connecting the outputof the ballistic computing means representing the flight period to theinput members of the said multipliers settable in accordance with theperiod of time of flight of the projectile.

4. A closed system re control computer, for a gun firing at a targetapproaching at a constant height above a horizontal plane, comprising avector analyzer including a settable vector member representative of thedirect range and elevation angle of the target position at an observinginstant and component members movable to positions representative of thehorizontal range and height components of the target position, amultiplier settable in accordance with the sum of a selected preparationperiod of time and the period of the time of flight of the projectileand the speed of the target for positioning an output in accordance withthe change in horizontal range during the combined preparation andflight periods, a secondmultiplier settable inaccordance with the ilightperiod and the speed of the target for positioning an output inaccordance with the change in horizontal range of the target during theperiod of time of flight of the projectile, means for combining themovements of the outputs of said multipliers and the movement of thehorizontal range member for moving a pair of elements in accordance withthe horizontal ranges of the target at the end of the respectiveperiods, a pair of vector means settable by the movements of therespective elements and the height member of the vector analyzer fordetering the angles of elevation of the target at the end of therespective periods, means for combining the outputs of said pair ofvector means for determining the vertical angular deflection, ballisticcomputing means settable in g accordance with the position of theelement representing the horizontal range of the target at the end ofthe flight period and in accordance with the height member fordetermining the super elevation of the gun and the flight period, meansoperably connecting the output of the ballistic computing meansrepresenting the flight period to the input members of the saidmultipliers settable in accordance with the period of time of flight ofthe projectile, and means settable in accordance with the position ofthe output of the ballistic computing means representing the superelevation for determining the angle of drift of the projectile.

5. A closed system re control computer, for a gun firing at a targetapproaching at a constant height above a horizontal plane, comprisingmembers movable to positions in accordance with the horizontal range andthe height of the target, a multiplier settable in accordance with thesum of a selected preparation period of time and the period of the timeof flight of the projectile and the speed of the target for positioningan output in accordance with the change in horizontal range during thecombined preparation and flight periods, a second multiplier settable inaccordance with the flight period and the speed Aof the target forpositioning an output in accordance with the change in horizontal rangeof the target during the period of time of flight of the projectile,means for combining the movements of the outputs of said multipliers andthe movement of the horizontal range member for moving a p air ofelements in accordance with the horizontal ranges of the target at theend of the respective periods, a pair of vector means settable by themovements of the respective elements and the height member fordetermining the angles of elevation of the target at the end of therespective periods, means for combining the outputs of said pair ofvector means for determining the vertical angulamdeggztion, ballisticcomputing means settable in accordance with the position of the elementrepresenting the horizontal rangengfwthe target at the end of the flightperiod andin accordance with the height member for determining theflight period.

GEORGE A. CROWTHER.

